G.4 Continuous Stage Recording
The location of water level recorder intakes is defined in the fabrication sketches for the two types of flumes listed and described earlier. Descriptive information on H-flumes (Figure G-3) is added in Figure G-4 with the associated dimension table. Related discharge tables are included in Appendix V. The stilling well for use with these flumes is normally mounted against the outer face of the prefabricated flume and centered opposite the flumes point of measurement. This permits the use of a very short easily cleared intake pipe which should be threaded and screwed through a double thickness of stilling well wall which is drilled and tapped to suit.
Note: Assuming ABS pipe is used for both stilling well and intake (metal pipe should be avoided as rapid heat conduction will result in frost formation) all fabrication can be accomplished on site. To form a double thickness wall, cut a patch from a length of scrap pipe (same diameter); using the correct solvent/glue and two large hose clamps, bond the patch in place.
Note: A threaded socket (and removable threaded plug) at the outer end of the intake can facilitate the sealing of the stilling well. The well can be pumped out when the station is deactivated over the Winter. Both well and intake will remain ice free making reactivating in the Spring less onerous.
The base of the stilling well should be positioned at least 15 cm below the floor of the flume.
In some instances Montana (Figure G-5) or Parshall flumes have been installed at sites where the maximum flume capacity may occasionally be exceeded. If these events are quantified by current meter measurements, a reference gauge and recorder installed upstream will provide a more complete station record. A flume gauge is provided and both gauge readings recorded at each station visit. Installation requirements for an upstream gauge are the same as for weirs, see Section G.3.3.
Stilling wells should be installed in the weir pond against a stabilized vertical bank or wall. The well must be secured near the base and above the high water elevation. The reference gauge and intake must be positioned upstream of the crest at a distance 3 to 4 times the maximum height of water over the crest (to avoid drawdown effect).
Sample 120 V-notch weir is shown in Figure G-6.
Figure G-3. 2.5 foot H Flume set in concrete filled sacks. Cuisson Creek above Gibraltar Mine.
Figure G-4. Dimensions of HL-type (top) and H-type (bottom) Flumes.
Figure G-5. 6-inch Montana Flume set in concrete sack bulkhead. Bidwell Creek above Chilko River.
Figure G-6. 120° stainless steel weir plate set in re-enforced concrete. Whitehead Creek below Whitehead Lake (Summerland District water supply).
